The proposed studies are focused on the temporal integration of excitatory and inhibitory synaptic events in primary visual cortex. The global hypothesis is that cellular and network mechanisms establish windows of time in which synchronous inputs are especially efficacious and asynchronous inputs are suppressed. An additional hypothesis is that these synaptic mechanisms serve to maintain the precision of spike timing of cortical cells at the same level seen in their thalamic afferents. The responses of cells in visual cortex to stimulus pairs spanning a range of temporal separations will be obtained in both extracellular and intracellular experiments. The extracellular studies will establish the full range of these phenomena for cells of all types in all layers. The intracellular studies will be directed at establishing the rules for synaptic integration and their mechanistic substrates at both biophysical and synaptic levels. This will be achieved in part by coupling presentation of visual stimuli with current injection for the identification of synaptic reversal potentials and the time courses of excitatory and inhibitory conductances. These basic experiments will be extended by the use of QX314 to block active membrane channels and altered CI" concentration in the pipettes to shift the reversal potential of inhibition. These studies will be conducted with both simple and complex cells and with cells possessing a wide variety of intrinsic electrophysiological properties. The rules and mechanisms so identified will be related to the reliability and precision of spike trains elicited by temporally rich stimuli. While much has been learned about what computations various areas of cerebral cortex are involved in, our understanding about how these computations are effected is rudimentary at best. The proposed studies will break new ground in term of revealing and understanding mechanisms by which visual cortex processes rapidly changing messages from the two eyes. This will be relevant to studies of cerebral cortex in general and specifically to how visual cortex processes signals elicited by microsaccadic eye movements known to be required for normal sight.